Automotive interior materials produced by stamping-mold process include door trim, rear package trim, sheet back garnish, instrument panel and the like.
A substrate for such automotive interior material as mentioned above generally is formed from a composition comprising polypropylene as a major component and talc or the like as a filler in an amount of 0 to 30% by weight.
The substrate is provided with rib or boss and has high rigidity, and is laminated with a skin material to form a composite. The stamping-mold process for preparing the above automotive interior material is a rational molding process to prepare composites in which molding steps are more simplified as compared with injection molding process.
However, the stamping-mold process conventionally used has such a problem that the substrate has a density of 0.91 to 1.1 g/cm.sup.3 and the resulting molded article is heavy. Today, it is a very important theme to reduce weight of automobiles in view of improvements in automotive fuel cost and environmental problems.
The above-mentioned stamping-mold process in which the skin material and the substrate can be integrally molded at the same time is an advantageous molding process from the viewpoint of cost. The stamping-mold process can be carried out at a lower pressure as compared with the injection molding, so that in this view point, this stamping-mold process is suitable for foaming the substrate as weight-reduction means.
In the conventional stamping-mold process, however, satisfactory foaming has been hardly obtained so far.
Accordingly, there has been eagerly desired an advent of a process capable of preparing composite foamed molded article of lightweight and having high rigidity utilizing the stamping-mold process.